1. Field of the Invention
The present invention relates to air conditioner, and more particularly, to a multi-type air conditioner and a method for controlling same, which can improve reliability of a compressor and system efficiency.
2. Discussion of the Related Art
In general, the air conditioner cools or/and heats rooms as the air conditioner performs steps of compression, condensing, expansion, and evaporation of refrigerant. In air conditioning systems, there are cooling air conditioner for supplying cold air to the room by operating a refrigerating cycle only in one direction, and cooling/heating air conditioner for supplying cold or warm air to the room by operating the refrigerating cycle in either direction, selectively.
Moreover, there are general air conditioners in which one indoor unit is connected to one outdoor unit, and multi-type air conditioners in which a plurality of indoor units are connected to one outdoor unit. In the meantime, the multi-type air conditioner may have one of more than one outdoor unit.
The multi-type air conditioner having one of more than one outdoor unit is provided with at least one compressor mounted on the outdoor unit. As the compressor, a single speed compressor of which operating frequency is constant, or a variable speed compressor of which operating frequency varies, is used.
However, the multi-type air conditioner having an outdoor unit with a plurality of compressors mounted thereon has the following problems.
That is, if the air conditioner is put into operation, there has been a problem of non-uniform distribution of oil among the plurality of compressors caused by differences of suction pressures of the compressors. Consequently, a compressor having a relative shortage of oil experiences drop of performance, to impair reliability. If the compressor is operated continuously in a state of oil shortage, the compressor is liable to burn. Moreover, the drop of performance of the compressor leads to drop an overall efficiency of the multi-type air conditioner, resulting to impair a cooling/heating performance.